1. Field of the Invention
The present invention relates to a piezoelectric resonator such as a quartz crystal resonator or the like, and a method of producing the same. Particularly, the present invention relates to the technique of electrically connecting electrodes formed on a resonator piece and preventing a short circuit.
2. Description of Related Art
Of various flexural vibration mode, longitudinal vibration mode, or torsional vibration mode piezoelectric resonators, for example, as shown in FIG. 11, a tuning fork type quartz crystal resonator comprises a piezoelectric resonator piece 1002 comprising a sheet-shaped quartz crystal piece in which two arms 1022 and 1023 are extended from a base 1021, internal terminals 1031 of a plug 1030 being connected to the base 1021 of the piezoelectric resonator piece. As shown in FIGS. 12(A) and 12(B) which are perspective views of the piezoelectric resonator piece 1002 used in a piezoelectric resonator (tuning fork type quartz crystal resonator) as viewed from the upper side and the lower side, respectively, two electrode patterns 1040 are formed with a predetermined gap therebetween on each of the upper side 1025 and the lower side 1026 of the arms 1022 and 1023 of the piezoelectric resonator piece 1002 to form exciting electrodes 1045. In FIGS. 12(A) and 12(B), in order to discriminate the two electrode patterns 1040, one of the electrode patterns 1040 is shown by lines inclined to the right, the other electrode pattern being shown by lines inclined to the left.
Since the exciting electrodes 1045 are formed on each of the upper side 1025 and the lower side 1026 of the piezoelectric resonator piece 1002, the exciting electrodes 1045 formed on the upper side 1025 of the piezoelectric resonator 1002 are electrically connected to the exciting electrodes 1045 on the lower side 1026 through conduction electrodes 1046 respectively formed on the edges 1251, 1252, 1253 and 1254 of the upper side 1025, the edges 1261, 1262, 1263 and 1264 of the lower side 1026, and the sides 1271 and 1272. Therefore, portions of the electrode patterns 1040, which are formed on the base 1021, are used as mounts, and the inner leads 1031 are electrically connected to the mounts with solder or a conductive adhesive so that an AC voltage is applied to the exciting electrodes 1045 through the inner leads 1031 to vibrate the arms 1022 and 1023 at a predetermined frequency.
In the piezoelectric resonator 1001 having the above construction, in some cases, the electrode patterns 1040 are formed in a chromium single layer. However, in order to decrease the electric resistance of the electrode patterns 1040, a noble metal layer such as a gold electrode layer, a silver electrode layer, or the like is used. However, the direct formation of a gold electrode layer on the surface of the piezoelectric resonator piece 1002 deteriorates adhesion between the piezoelectric resonator piece 1002 and the gold electrode layer. Therefore, as shown in FIG. 13(A) which is a sectional view taken along line IV-IV′ of FIG. 12 showing the piezoelectric resonator piece 1002 used in a conventional piezoelectric resonator, under metal layers 1041 each comprising a chromium layer are formed as under layers even when gold electrode layers 1042 are used for the electrode patterns 1040.
On the other hand, in the arms 1022 and 1023 of the piezoelectric resonator (quartz crystal resonator) 1, the gap between the electrode patterns 1040 is as small as the μm order, and thus a short circuit readily occurs between the electrode patterns 1040. Therefore, as shown in FIGS. 13(B) and 13(C) which are sectional views taken along lines V-V′ and VI-VI′, respectively, of FIGS. 12(A) and 12(B), surface protecting films 1047 each comprising a silicon oxide film are formed on the surfaces of the electrode patterns 1040 by sputtering. However, the silicon oxide films (the surface protecting films 1047) have poor adhesion to the gold electrode layers 1042, and thus the gold electrode layers 1042 are removed from the arms 1022 and 1023 to expose the under metal layers 1041 each comprising a chromium layer so that the surface protecting films 1047 are formed on the under metal layers 1041.
As shown in FIG. 13(A), the gap between the electrode patterns 1040 in the base 1021 side is large, and thus no short circuit occurs between the electrode patterns 1040. Also, from the viewpoint of soldering between the inner leads 1031 of the plug 1030 and the mount, as shown in FIG. 11, the gold metal layers 1042 are preferably formed. Therefore, as shown in FIG. 13(A), each of the electrode patterns 1040 has a two-layer structure comprising the under metal layer 1041 and the gold electrode layer 1042 without the surface protecting film 1047.
Furthermore, in the conventional piezoelectric resonator 1001, the exciting electrodes 1045 are formed on each of the upper side 1025 and the lower side 1026 of the piezoelectric resonator piece 1002, and the exciting electrodes 1045 formed on the upper side 1025 of the piezoelectric resonator 1002 are electrically connected to the exciting electrodes 1045 on the lower side 1026 through the conduction electrodes 1046 respectively formed on the edges 1251, 1252, 1253 and 1254 of the upper side 1025, the edges 1261, 1262, 1263 and 1264 of the lower side 1026, and the sides 1271 and 1272. However, each of the electrode patterns 1040 corresponding to the conduction electrodes 1046 comprises only the under metal layer 1041 comprising a chromium layer, thereby causing a problem in that the exciting electrodes 1045 formed on the upper side 1025 and the exciting electrodes 1045 formed on the lower side 1026 are readily brought into an open state. Namely, the under metal layer 1041 comprising a chromium layer which forms each of the conduction electrodes 1046 comprises a hard film, and thus cracks occurs in the curved or bent portions 1276, 1277, 1278 and 1279 of the sides 1271 and 1272 of the piezoelectric resonator piece 1002 to easily cause disconnection. In forming a mask for partially etching the gold electrode layers 1042 formed on the surfaces of the under metal layers 1041 comprising chromium layers, in some cases, misalignment occurs to cause the chromium layers (the under metal layers 1041) to be etched off by etching the gold electrode layers 1042, thereby producing defects in the conduction electrodes 1046 comprising chromium layers (the under metal layers 1041). In this way, the exciting electrodes 1045 on the upper side 1025 of the piezoelectric resonator piece 1002 and the exciting electrodes 1045 on the lower side 1026 thereof are brought into an open state by disconnection of the conduction electrodes 1046, causing the problem of increasing the CI value (crystal impedance/the resistance value when the mechanical vibration system of a resonator is represented by an equivalent circuit comprising a series resonant circuit containing resistance, capacitance and impedance, and parallel capacitance provided in parallel with the series resonant circuit) or disenabling oscillation.